Class Ia MHC-Deficient BALB/c Mice Generate CD8 T Cell-Mediated Protective Immunity Against Listeria

CD8 T cells are required for protective immunity against intracellular pathogens such as Listeria monocytogenes. In this study, we used class Ia MHC-deficient mice, which have a severe reduction in circulating CD8 T cells, to determine the protective capacity of class Ib MHC-restricted T cells during L. monocytogenes infection. The Kb/Db/ mutation was backcrossed onto a C.B10 (BALB/c congenic at H-2 locus with C57BL/10) background, because BALB/c mice are more susceptible to Listeria infection than other commonly studied mouse strains such as C57BL/6. C.B10 Kb/Db/ mice immunized with a sublethal dose of L. monocytogenes were fully protected against a subsequent lethal infection. Adoptive transfer of Listeria-immune splenocyte subsets into naive Kb/Db/ mice indicated that CD8 T cells were the major component of this protective immune response. A CD8 T cell line isolated from the spleen of a Listeria-infected class Ia MHC-deficient mouse was shown to specifically recognize Listeria-infected cells in vitro, as determined by IFN- secretion and cytotoxicity assays. Adoptive transfer of this T cell line alone resulted in significant protection against L. monocytogenes challenge. These results suggest that even a limited number of class Ib MHC-restricted T cells are sufficient to generate the rapid recall response required for protection against secondary infection with L. monocytogenes. The Journal of Immunology, 2003, 171: 291–298. L isteria monocytogenes is a Gram-positive bacterium with aunique intracellular life cycle that allows it to spread fromcell to cell without being exposed to the extracellular en-vironment (1). Within 15 min of i.v. inoculation of a mouse, 90% of the bacteria resides in the liver, and most of the remainin